The present invention relates to a process for manufacturing an elastically stretchable and contractible composite sheet comprising a web capable of elastic stretch and contraction and a fibrous web capable of inelastic extension.
Japanese Patent Publication No. 1996-504693A discloses a multi-layered elastic panel, as one example of this type of composite sheet, and a process of manufacturing the same. This manufacturing process of a multi-layered elastic panel involves arranging a rubber elastic layer and an inelastic fibrous layer, one over another, joining them intermittently, extending the combination up to the vicinity of a breaking extension limit of the inelastic fibrous layer and finally relaxing the combination from tension.
In the composite sheet (elastic panel) obtained via the above-specified known manufacturing process, the rubber elastic layer after removal of the tension is unable to return to its original dimension. The resulting difference in dimension sometimes produces a permanent strain in the composite sheet. Such a permanent strain is a first factor that makes the composite sheet larger in dimension along a direction of extension than before it is extended. Also, the inelastic fibrous layer when extended undergoes plastic deformation so that its dimension after extension is made larger than before extension. When the rubber layer is released from the tension, this dimensional difference causes the inelastic fibrous layer to increase its apparent bulk. The increased bulk then becomes a second factor that makes the composite sheet larger in dimension than before extension by restraining the rubber elastic layer from recovering, i.e., by restricting elastic contraction thereof. By these first and second factors, the composite sheet when again extended to the vicinity of a breaking extension limit of the inelastic fibrous layer exhibits a lower percentage extension than when initially extended to the vicinity of the breaking extension limit of the inelastic fibrous layer.
It is an object of the present invention to provide a process for manufacturing a composite sheet which can reduce the influence of the above-described first factor encountered in the known manufacturing process and thus widen the range that permits elastic stretch and contraction of the sheet.
To achieve this object, the present invention is directed to a process for manufacturing a composite sheet capable of elastic stretch and contract in one direction, which includes the steps of continuously feeding a first web capable of elastic stretch and contraction in the one direction and having a top surface and a bottom surface, continuously feeding a second web capable of inelastic extension and composed of thermoplastic synthetic fibers on at least one surface of the first web and joining the first and second webs in an intermittent manner along the one direction.
In the above-described manufacturing process of the composite sheet, the present involves the steps of:
(a) feeding the first web continuously in the one direction and extending the first web in the one direction within the range that permits elastic stretch and contraction of the first web;
(b) allowing the extended first web to retract by the action of an elastic contraction force of the web; and
(c) superimposing the second web on at least one surface of the first web after retraction and joining the first and second webs in an intermittent manner along the one direction.
In one embodiment of this invention, subsequent to the step (c), the following steps are further included:
(d) a secondary extension step wherein the joined first and second webs are extended in the one direction within the range that permits elastic stretch and contraction of the first web; and
(e) a secondary contraction step wherein the extended first and second webs are allowed to retract by the action of an elastic contraction force of the first web.